1. Field of the Invention
The present invention relates to the field of vehicular wheelchair lifts for persons who are physically challenged or otherwise have limited mobility. More particularly, the present invention relates to the field of vehicular wheelchair step lifts with a manually foldable platform.
2. Description of the Prior Art
Specifically, automatic folding and unfolding of vehicle steps into a platform of a wheelchair lift is well known in the art. These mechanisms involve relatively complicated structures for making them more automatic and often not sufficiently reliable.
United States Patent No. Re. 33,595 issued to Sullivan et al. on May 28, 1991 discloses a wheelchair lift which utilizes a step configuration platform. It comprises a plurality of individual panels which are hinged together and extended into a geometrical plane rather than a step structure. The resulting platform is then elevationally adjusted by the driver to move the platform and a wheelchair victim on the platform, between the curb and bus floor level. The wheelchair lift further comprises a hydraulic drive for deploying the mechanisms between step and platform mode, a safety barrier structure which defines an extension of the platform to the curb level when it is dropped from its safety barrier mode, a safety locking mechanism and a stabilizing chain. The disadvantage with this platform is that it is fully automatic in folding and unfolding of the platform and the mechanism to fold and unfold the platform involves complicated structures.
U.S. Pat. No. 4,606,433 issued to Smalley et al. on Aug. 19, 1986 discloses a step convertible platform lift. It comprises a frame mounted in a rectangular notched-out floor section, which the frame comprises corner posts which also act as guides for up and down movement of the platform lift. The movable platform comprises three sections foldable into a lower step, a riser and an upper step, which sections are pivoted on shafts along their adjacent edges. The pivot shaft for upper step section and riser also is connected to reciprocating motor means for raising and lowering the platform. Lever extensions are fixedly attached to the ends of the riser, which are pivotally connected to other reciprocating motor means which unfolds the riser from an acute angle under the upper step section into a position coplanar with the upper step and at the same time moves the lower step section horizontally outwardly and upwardly into the same coplanar to form the platform. Again, the disadvantage with this platform is that it is fully automatic in folding and unfolding of the platform and the mechanism to fold and unfold the platform involves complicated structures.
U.S. Pat. No. 5,316,432 issued to Smalley et al. on May 31, 1994 discloses a wheelchair lift with an automatic barrier. Steps are convertible into a platform of an elevator for wheelchairs, during which conversion a barrier is automatically raised from the bottom step to be at the outer edge of the platform. The barrier is operated by an extensible link under the bottom step, which link is connected between the barrier and a crank arm keyed to an oscillatible transverse shaft under the inner part of the bottom step. Two additional crank arms are keyed to the ends of this shaft and are connected to a frame for a step or riser to oscillate said shaft when the steps are extended and unfolded into their platform position. The extendible link extends the barrier into a ramp when the platform is in its lowest position for access by a wheelchair. Reciprocating motors such as hydraulic pistons extend, retract, fold and unfold the panels that form the steps and their intermediate risers. When the step panels are in the platform position, additional reciprocating motors raise and lower the platform as an elevator. Stabilizing chains and rack and pinion gears insure uniform motion of the sides of the elevator and of the extendible bottom step. Still again, the disadvantage with this platform is that it is also fully automatic in folding and unfolding of the platform and the mechanism to fold and unfold the platform involves complicated structures and requires relatively large vertical space under the platform to accommodate the automatic actuating means and mechanism.
It is highly desirable to have a very efficient and also very effective design and compact construction of a vehicular wheelchair step lift which is fully automatic controlled in raising and lowering the lift movements with a manually controlled foldable platform.